Genmab Acquires Merus in $8 Billion Deal, Gaining Promising Cancer Bispecific Antibody

Danish pharmaceutical company Genmab has agreed to acquire Netherlands-based biotech Merus for $8 billion, a move that significantly bolsters Genmab's oncology pipeline and accelerates its transition to a fully integrated biopharma company. The deal, announced on September 29, 2025, centers around Merus' lead asset petosemtamab, a bispecific antibody showing strong potential in head and neck cancer treatment.

Deal Details and Strategic Rationale

Genmab will pay $97 per share in cash for Merus, representing a 41% premium to the biotech's closing price on Friday. The acquisition aligns with Genmab's long-term strategy to shift towards a wholly-owned model and build a pipeline of proprietary late-stage cancer assets.

Jan van de Winkel, CEO of Genmab, stated, "The proposed acquisition of Merus clearly aligns with our long-term strategy. It has the potential to significantly accelerate our evolution into a global biotechnology leader by providing durable growth for the company well into the next decade."

Petosemtamab: A Potential Game-Changer in Cancer Treatment

The centerpiece of the acquisition is petosemtamab, Merus' bispecific antibody targeting EGFR and LGR5. The drug has shown promising results in clinical trials, particularly for head and neck squamous cell carcinoma:

• In a Phase II trial, petosemtamab combined with Merck's Keytruda demonstrated a 79% overall survival rate at 12 months.
• The combination also achieved a 63% overall response rate and a median progression-free survival of 9 months.

These results have led analysts to describe petosemtamab as having a "best-in-disease profile" for head and neck cancer, with the potential to become a standard of care when combined with Keytruda.

Genmab projects that petosemtamab could generate $1 billion in annual sales by 2029, with multi-billion-dollar revenue potential thereafter. The company aims to bring the drug to market by 2027, pending successful completion of ongoing Phase III trials expected to read out in 2026.

Implications for the Biopharma Industry

The Genmab-Merus deal is seen as a positive sign for the wider biopharma industry, potentially spurring broader M&A activity. It follows closely on the heels of Pfizer's $4.9 billion acquisition of Metsera last week, indicating a possible uptick in deal-making after a period of relatively subdued M&A activity.

For Genmab, the acquisition adds to its growing portfolio of antibody-based therapies, which includes partnerships on successful drugs like Darzalex (with Johnson & Johnson) and Tivdak (with Seagen). The addition of petosemtamab strengthens Genmab's position in the competitive oncology market and supports its evolution into a fully integrated biotechnology company.